This invention refers to a high-pressure mixing head for mixing fluid components, in particular for mixing chemical components suitable for forming polyurethane foams which are then fed into a mold.
The mixing head of the aforesaid kind, usually comprises a body having a mixing chamber into which open out the injectors for feeding the individual components, and an outlet duct axially aligned with the mixing chamber in which a control member in the form of a movable plunger slides from a retracted position in which it allows the components to be fed into the mixing chamber, to an advanced position in which it prevents the components from entering and at the same time expelling the residual mixture remaining in the mixing chamber and in the outlet duct; a mixing head of this type is known, for example, from DE PS 2007935.
At the end of each mixing cycle, the individual components can be made to recycle towards their respective tanks by means of per se known rotating recycling valves, or slide valves, or in any other way. From a previous patent IT 21022 A/78 of the same applicant, it is also known to provide a mixing chamber, small in volume and very limited in length, arranged at right angles and in direct communication with the outlet duct in order to improve the mixing degree.
In all the known mixing heads, the disposition of the mixing chamber is fixed with respect to the outlet duct, since both are made in the body of the head or in parts connected thereto.
In such heads the mixing is achieved by means of the collision of the jets of components, in correspondence with the feed injectors, after which the flow of mixture remains substantially unchanged; in order to improve the mixing degree, it has also been suggested to use restrictors in the outlet duct, DE A-2.007934 and DE A-2.612.812, thereby involving a complex structure and complicating the functioning of the head. Moreover, on the known mixing heads, the distance between the injection nozzles depends upon the crosswise dimensions of the mixing chamber, whereas it would be desirable to keep the nozzles as close as possible for satisfactory mixing. A reduction in the crosswise dimensions of the mixing chamber however cannot be carried beyond certain limits due to the fact that it would excessively reduce the strength of the cleaning member in the chamber itself; furthermore, it would make it difficult to make component recycling channels in the cleaning member with a sufficient cross-sectional area of flow, and would introduce excessive additional pressure losses, during the recycling phases of the components which would have a negative effect during the mixing phases.
A scope of this invention is to provide a high-pressure mixing head for at least two components, of completely new design, capable of providing a high degree of mixing by simple means, which make it possible to render the disposition and the distance between the injectors independent, with respect to the mixing chamber, the dimensions and volume of which can be suitably calculated in accordance with the desired rates of flow. A further scope of the invention is to provide a mixing head, as defined, in which the recycling channels for the components are provided outside the chamber itself, and can consequently be made with suitably-sized cross sectional areas for recycling the individual components, whilst keeping pressure losses to a minimum.
A still further scope of this invention is to provide a high-pressure mixing head capable of greatly improving the degree of mixing of the components, by providing subsequent mixing areas, whilst keeping the structure and the functioning of the head extremely simple. A still further scope of this invention is to provide a mixing head, of the aforementioned type, in which it is possible to avoid any contamination whatsoever of the chemical components and/or the mixture, by the fluids actuating the hydraulic control members.